The first vol. of a trilogy; the second is Witch water and the third is The witch herself
Book Description: Lynn suspects her sister Judith is being taught witchcraft by old Mrs. Tuggle who lives next door. Lynn and her friend Mouse try to prove Mrs. Tuggle's guilt, but after no luck, they give up--until one night when Mrs. Tuggle comes over to babysit Lynn's little brother, Stevie. Can Lynn save Stevie from being sacrificed?